first of all check that the machine is threaded correctly,the bobbin case as well as the main tension.Make sure that the thread is pulling smoothly and not snagging, again also check the same with your bobbin case.
Check that you have the needle in the correct way,when you try the machine again make sure that it is not trying to feed the material whilst the needle is in its lowest position if it is then your feed timing is out and you will need a mechanic to adjust it for you.
If its feeding the fabric correctly then try adjusting the main tension to stop the looping,you also have a tension screw on the bobbin case you can try to adjust,to make the tension tighter turn the screw clockwise and anti-clockwise to slacken the tension.
Hope this helps.
D.Hooper
November 2007